GARRY DELONG / SCIENCE PHOTO LIBRARY GARRY DELONG / SCIENCE PHOTO LIBRARY
Light micrograph of a section through an oak gall (oak apple), likely a reaction to an insect parasite. As shown here, galls often contain cells with inclusions of pigmented material, often tannin, which was until the 20th century in the production of a very permanent ink. Also present are several vascular bundles. Magnification 28x when printed at 10 cm.
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